The isolation of micro-organisms from the oil-in-water Aqueous Cream BP, has been examined using a variety of solvent systems to disperse the cream prior to membrane filtration or direct inoculation. Pour-plate methods which utilize combinations of either peptone-water (containing 5% w/v polysorbate 80) or nutrient broth (containing 4'3, w/v Lubrol W) provided the most efficient recovery of Pseudomonas aeruginosa but still allowed less than 20°, recovery. White spirit and isopropyl myristate allowed no recovery when used as dispersants. Recoveries of P . aeruginosa varied according to the source of the cream. A combination of l?& w/v polysorbate 80 in 0.1 O 0 w/v peptone-water and membrane filtration allowed 63.256 wlv and 67.0% w/v recoveries respectively of Aspergillus niger and Candida albicans from unpreserved aqueous cream, but gave unreproducible results for Escherichia coli and P . aeruginosa. Chlorocresol 0.1 yo w/v) did not meet the British Pharmacopoeia1 requirements for efficacy of antimicrobial preservatives when tested against C . albicans using membrane filtration to isolate the micro-organism.
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